Transformation of the Structure and Properties of Laser-Irradiated Steels Under External Thermal Deformation Action

Processes of structure transformation in irradiated steel surface layers, occurring in tribological systems under external thermal deformation action, are considered. It is established that by varying laser radiation regime parameters it is possible to use the structural adaptability phenomenon of irradiated zones in steels intentionally, and to obtain structures within them that have a different degree of adaptation to external loading conditions during operation. This has a positive effect on heat and wear resistance of irradiated products for various functional purposes. It is shown that irradiation with a radiation power density of 80–120 MW/m² (without melting) leads to strain ageing of laser-hardened martensite. This contributes to creation upon working surfaces of products whose structural state is almost indifferent to thermal deformation loading and is resistant to softening for a long time. With an irradiation power density of 120–170 MW/m² (with melting), surface structures are formed that adapt to external effects. Laser-hardened austenite transforms into strain-induced martensite under thermal loading action. At the same time, martensite strain ageing occurs within laser irradiation zones. Fine carbides, 2–10 nm in size, precipitate during this time upon crystal structure defects with formation of a precipitate texture. As a result material heat resistance after laser irradiation increases by 50–100°C, and wear resistance by a factor of 2–4. Based upon the experimental results, maps of regression modeling of the laser surface hardening production process are constructed. This permits selection of regimes for both laser processing and operating conditions, and the subsequent product tempering temperature for various functional purposes.